This invention relates to sulphoxonium salts and to compositions comprising a cationically-polymerisable material and a sulphoxonium salt. It also relates to the polymerisation of such compositions by means of actinic radiation and to the optional further crosslinking of photopolymerised products so obtained by means of heat in the presence of heat-curing agents, to the polymerisation of such compositions by the effect of heat alone, and to the use of the compositions as surface coatings, in printing plates, in printed circuits, and in reinforced composites, and as adhesives.
For a number of reasons, it has become desirable to induce polymerisation of organic materials by means of actinic radiation. Employing photopolymerisation procedures may, for example, avoid the use of organic solvents with their attendant risks of toxicity, flammability, and pollution, and the cost of recovering the solvent. Photopolymerisation enables insolubilisation of the resin composition to be restricted to defined areas, i.e., those which have been irradiated, and so permits the production of printed circuits and printing plates or allows the bonding of substrates to be confined to required zones. Further, in production processes, irradiation procedures are often more rapid than those involving heating and a consequential cooling step.
It has been known for some years that certain aromatic diazonium salts undergo decomposition on exposure to actinic radiation and that, if the salt is mixed with a cationically-polymerisable substance, then the Lewis Acid which is generated in situ on irradiation induces polymerisation (see, for example, British Pat. No. 1,321,263). However, the diazonium salts are not entirely satisfactory: the pot-life of the mixture of diazonium salt and cationically-polymerisable substance is often too short, particularly in daylight, and secondly, nitrogen is generated during liberation of the Lewis Acid catalyst, which evolution of gas restricts the range of processes in which the catalysts may successfully be employed.
Numerous proposals have therefore been made for the replacement of these diazonium salts by others which, while liberating an acid catalyst on irradiaton, do not also evolve nitrogen: particularly intensively studied have been onium salts of sulphur, and iodonium salts.
Thus, it has recently been disclosed, in British Pat. No. 1,516,511 and its United States equivalent, U.S. Pat. No. 4,058,401, that a mono-1,2-epoxide, an epoxide resin (i.e., a substance containing on average more than one 1,2-epoxide group), or a mixture thereof, may be polymerised or cured by means of a radiation-sensitive aromatic onium salt of oxygen, sulphur, selenium, or tellurium present in an amount capable of effecting the polymerisation or cure of the epoxide (or polyepoxide) by release of a Bronsted Acid catalyst when exposed to radiant energy. The only such salts described in the specification are of the formula ##STR2## where R denotes a monovalent aromatic radical,
R.sup.1 denotes an alkyl, cycloalkyl, or substituted alkyl group, PA1 R.sup.2 denotes a polyvalent aliphatic or aromatic radical forming a heterocyclic or fused ring structure, PA1 X denotes oxygen, sulphur, selenium, or tellurium, PA1 M denotes an atom of a metal or metalloid, such as antimony, iron, tin, bismuth, aluminum, gallium, indium, titanium, zirconium, scandium, vanadium, chromium, manganese, boron, phosphorus, or arsenic, PA1 Q denotes a halogen radical, PA1 a denotes 0, 1, 2, or 3, PA1 b denotes 0, 1, or 2, PA1 c denotes 0 or 1, the sum of a+b+c being 3 or the valency of X, PA1 d denotes (e-f), PA1 f is the valency of M, and is an integer of from 2 to 7, and PA1 e is more than f and is an integer of up to 8. PA1 R.sup.1 denotes a divalent aromatic radical, PA1 R.sup.2 denotes a polyvalent aliphatic or aromatic radical forming a heterocyclic or fused ring structure, PA1 R.sup.4 denotes an alkyl, alkoxy, cycloalkyl, or substituted alkyl radical, PA1 R.sup.5 denotes a polyvalent radical forming an aromatic, heterocyclic or fused ring structure, PA1 M denotes an atom of a metal or a metalloid, PA1 X denotes a halogen radical, PA1 Z denotes a nitrogen, phosphorus, arsenic, bismuth, or antimony atom, PA1 a denotes 0 or 2, PA1 b denotes 0 or 1, where a+b=2 or the valency of iodine, PA1 c denotes 0 or 3, PA1 d denotes 0 or 2, PA1 e denotes 0 or 1, such that (c+d+e)=3 or the valency of sulphur, PA1 f is an integer of from 0 to 4, PA1 g is 0, 1, or 2, PA1 h is 0, 1, or 2, such that (f+g+h)=4 or the valency of Z, PA1 j is k-m, PA1 m is the valency of M, being 2 to 7, and PA1 k is an integer of more than 1 but not more than 8. PA1 R denotes an aromatic hydrocarbon or heterocyclic group of 6 to 13 carbon atoms, which may be substituted, PA1 R.sup.1 denotes a divalent aromatic hydrocarbon or heterocyclic group, which may be substituted, PA1 a is 1 or 3, PA1 b is 0 or 1, PA1 S has a valency of 3, which may be satisfied by R alone or by a combination of R and R.sup.1, PA1 M denotes an atom of a metal or metalloid, PA1 Q denotes a halogen radical, and PA1 d is 4, 5, or 6.
Shortly afterwards, in British Pat. No. 1,518,141, and also in its corresponding U.S. Pat. No. 4,058,400, the same patentee disclosed that monomeric or prepolymeric, cationically polymerisable organic materials free from and 1,2-epoxide group, selected from vinyl monomers, vinyl prepolymers, cyclic ethers, cyclic esters, cyclic sulphides, cyclic amines, and organosilicon cyclics, can also be polymerised by exposing them to radiant energy in the presence of an effective amount of a radiation-sensitive onium salt of the Group VIA elements listed above. The only onium salts described are likewise of formula I above.
Still more recently, in its U.S. Pat. No. 4,102,687, the same patentee disclosed that the curing of urea-formaldehyde resins, melamine-formaldehyde resins, and phenolformaldehyde resins could be initiated by exposing them to ultraviolet radiation in the presence of a Group VIA onium salt, curing being completed by heating. Again, only the onium salts of formula I are mentioned.
Subsequent disclosures of this patentee concerning onium salts of sulphur have been confined to sulphonium salts.
Thus, British Pat. No. 1,535,492 describes the use of radiation-sensitive sulphonium salts of arylsulphonic, haloarylsulphonic, alkylsulphonic, and haloalkylsulphonic acids for the cationic polymerisation of epoxide resins, vinyl monomers and prepolymers, cyclic organic ethers, cyclic organic esters, cyclic organic sulphides, cyclic amines, and cyclic organic silicon compounds.
Its U.S. Pat. No. 4,139,385 discloses the use of sulphonium and other salts in the curing of polyolefins by means of polythiols. A polyethylenically unsaturated compound, such as diallyl phthalate, diallyl maleate, or triallyl cyanurate, is mixed with a polythiol, such as trimethylolpropane trithioglycollate or pentaerythitol tetra(3-mercaptopropionate) and, e.g., triphenylsulphonium hexafluoroarsenate or tetrafluoroborate, and then exposed to ultraviolet light. The salts used as catalysts are all of the formula ##STR3## where R denotes a monovalent aromatic radical,
Its West German Offenlegungsschrift No. 2 833 648 discloses that triarylsulphonium salts of formula ##STR4## can be used to initiate the curing, on irradiation, of an aliphatically-unsaturated composition containing a 1,2-epoxide group, such as glycidyl acrylate, or a mixture of an epoxide resin with an aliphatically-unsaturated substance such as methyl methacrylate, a polyester, or styrene. In formula V,
Its U.S. Pat. No. 4,136,102 describes various sulphonium salts containing a hexafluorophosphate, hexafluoroarsenate, or hexafluoroantimonate anion and their use in curing epoxide resins. They are stated to be also useful for the polymerisation of a variety of unspecified cyclic organic and cyclic organo-silicon compounds.
Its West German Offenlegungsschrift No. 2 730 725 discloses the photo-induced curing, by means of aromatic onium salts, of epoxide resin compositions which also contain a polyvinyl acetal. The only onium salts of sulphur indicated are those of formula I.
Its U.S. Pat. No. 4,081,276 describes a process for the formation of photoresist images, especially for printed circuit production, wherein a layer of a photoinitiator is exposed to radiant energy and then contacted with a cationically polymerisable material, e.g., an epoxide resin. Again, the only onium salts of sulphur cited are those of formula I above.
Another patentee has described, in Belgian Pat. No. 845 746, the photopolymerisation, using as catalyst an aromatic sulphonium salt or an aromatic iodonium salt, of mixtures comprising a compound having an epoxide functionality of more than 1.5 epoxide groups per molecule and a compound having hydroxy functionality of at least one.
This second patentee describes, in U.S. Pat. No. 4,090,936, photohardenable liquid compositions comprising
(a) an organic compound having an average epoxide functionality in the range of about 1 to 1.3,
(b) from about 3 to 50% by weight, calculated on the weight of (a), of an organic polymer which is compatible with (a) and has a glass transition temperature in the range of about -20.degree. C. to 105.degree. C., being a polymer derived from at least one acrylate or methacrylate monomer, or a copolymer of styrene and allyl alcohol, or a polyvinyl butyral polymer, and
(c) an aromatic complex salt photoinitiator which is an onium salt of a Group VA or Group VIA element or a halonium salt. The only onium salts of sulphur indicated are sulphonium salts.
Another disclosure of this second patentee, U.S. Pat. No. 4,069,054, relates to photopolymerisable compositions containing a cationically polymerisable monomer, an aromatic sulphonium compound, and an aromatic tertiary amine, aromatic tertiary diamine, or an aromatic polycyclic compound as a sensitiser.
An aromatic sulphonium salt, namely triphenylsulphonium hexafluorophosphate, has been used commercially for the photopolymerisation of epoxide resins.
We have now surprisingly found that cationically polymerisable materials can be polymerised by means of actinic radiation or heat in the presence of certain aromatic sulphonylsulphoxonium salts as catalysts.
Unlike compositions of the prior art containing sulphonium salts as catalysts, compositions of this invention do not liberate obnoxious mercaptan odours on irradiation.
We have further found that, contrary to what would be expected from the teachings of U.S. Pat. No. 4,102,687, urea-formaldehyde resins may be cured on irradiation in the presence of an aromatic sulphonylsulphoxonium salt of this invention without the need to apply heat.